Photochromism is a phenomenon that is drawing attention in these several years, and is a reversible action of a compound which quickly changes its color (called development of color) when it is irradiated with light containing ultraviolet rays such as sunlight or light of a mercury lamp and resumes its initial color (fading of color) when it is no longer irradiated with light but is placed in a dark place. The compound having this property is called photochromic compound. One of the uses of the photochromic compound may be to use it as a dimmer material for lenses of sunglasses.
In such an application, the photochromic compound must have photochromic properties which are, for example:    (1) Color changes stably when the developing of color and the fading of color are repeated (has a good repetitive color resistance);    (2) Has a small coloring degree (hereinafter called initial color) when placed in a state of not being irradiated with light; and    (3) Exhibits a high color fading rate when the compound is no longer irradiated with light.
In recent years, it has been urged to produce a photochromic compound which, by itself, develops a neutral tint such as gray, brown or green. The compound that develops a neutral tint must have two absorption bands (440 to 550 nm and 580 to 630 nm) in a wavelength region of visible light, and must have nearly the same absorption intensity ratio in each absorption band.
In order to satisfy the above requirement, a variety of photochromic compounds have heretofore been synthesized without, however, any particular common nature in their structures.
For example, U.S. Pat. No. 5,783,116 discloses a chromene compound represented by the following formula (A),

This chromene compound has only one absorption band and is not capable of developing color tone of a neutral tint and, further, has a problem of a small color fading rate.
Further, PCT Laid-Open WO 00/15628 discloses a chromene compound represented by the following formula (B),

This chromene compound satisfies the requirement of a color-developing spectrum of a neutral tint described above, and is capable of developing a neutral tint such as brown offering such a feature that the initial coloring is weak accompanied, however, by a defect of low color fading rate.
Japanese Patent Application No. 344762/2000 discloses a chromene compound represented by the following formula (C),

This chromene compound exhibits a high color fading rate but has a large difference in the absorption intensity between the two absorption bands. Therefore, this chromene compound develops a single color of blue only accompanied by a defect of large initial coloring.